1. Field of the Invention
This invention relates to an intake system for a multiple cylinder engine, and more particularly to an intake system for a multiple cylinder engine having an engine intake noise suppressing system for suppressing noise which is generated by the intake stroke of the engine.
2. Description of the Prior Art
Recently, the quietness of the engine has come to be highly required. In order to satisfy this requirement, there have been made various attempts to suppress the intake noise generated by resonance at a particular frequency which is caused due to pulsation of air in the intake passage.
For example, it has been proposed to connect a resonance muffler to the intake passage between the air cleaner and the intake ports, the resonance type muffler having a resonance frequency corresponding to the frequency of oscillation generated in the intake passage, as disclosed in Japanese Unexamined Patent Publication No. 54(1979)-9317. Further, it has been proposed to connect a resonance muffler to the intake passage upstream of the air cleaner, the resonance muffler having a resonance frequency corresponding to the frequency of oscillation generated in the intake passage, as disclosed in Japanese Unexamined Patent Publication 58(1983)-172451 and Japanese Unexamined Utility Model Publication No. 61(1986)-192560. Conventionally, the air cleaner generally has a relatively large volume and cuts off the intake noise. Accordingly, the provisions described above are made for the resonance which occurs in the intake passage upstream of the air cleaner or the intake passage downstream of the same.
However as the maximum output power of engines is increased, the discrete intake passages which connect the respective cylinders to the common intake passage have come to occupy a larger space in the engine room, and the volume of the air cleaner has been reduced. Especially in the fuel injection type engines, a small volume air cleaner is apt to be used. When the volume of the air cleaner, which functions as an expansion type muffler, is small, low frequency range intake noise cannot be cut off.